Offshore producing wells are subject to numerous natural hazards. These hazards vary with the geographical location of the well and the geological formation into which the well penetrates. Prior proposed well constructions provided for a very low well head profile on the seabed, the well head being connected to flowlines which conducted the production fluid to suitable storage or other distribution facilities located either on the seabed, on a surface platform means for transfer to a barge, or on shore. In some instances, the well construciton included an enlarged housing which extended into the seabed and provided a chamber for flow control means at a depth below the seabed so as to be unaffected by passage of ice masses or moving objects over and through the surface of the seabed. Such an enlarged housing and chamber will flow control means therein is shown in U.S. Pat. No. 3,866,676.
Other prior proposed completion systems for an offshore well have included placing control valves in a relatively large diameter caisson located below the sea floor. In such systems, a control head extended above the sea floor and the principal control valves were located in the caisson below the floor.
In such prior proposed systems the desire for a low profile well head means at the sea floor was to avoid damage caused by ship anchors, fishing nets, ice masses, or other things which might be dragged along a seabed and which would be likely to strike the exposed well head structures and flow lines.
In recent years, environmental considerations emphasized that ocean waters be freed from pollution by well fluids. In such prior proposed constructions, a mud slide or a shifting of the earth across the line of a well hole might cause breaking of the pipe conducting production fluid to the top of the well. In prior proposed construction including those having flow control means below the surface of the seabed, the flow control means were not located at a sufficient depth below the seabed to cut off leakage of production fluid in the event such a breakage occurred. Moreover, such prior proposed constructions were limited by cost and by the earth mass in the depth that such flow control means could be placed because of the requirement of using caissons of fairly large diameter such as 36 inches or chambers of even greater diameter.
In some prior production installations, a riser pipe extended from the well head at the sea floor to a platform means located thereabove. In severe storm conditions, it may become desirable to release the riser pipe so that damage to the platform structure and well equipment would be minimized. In prior proposed constructions, release of the riser pipe from the well head at the seabed was contemplated. Reconnection of the riser pipe to the well head under these circumstances was time consuming and difficult, particularly in deep water below diver depth.